1. Field of the Invention
The present invention relates to a spindle control circuit of an optical disk drive, and more particularly to a spindle control circuit of an optical disk drive for performing a constant linear velocity (CLV) control in accordance with a wobble signal.
2. Related Background Art
In a conventional optical disk drive, a spindle control for controlling the rotation of a spindle motor so as to maintain the rotation of an optical disk at a constant linear velocity is performed in accordance with a wobble signal picked up from the optical disk. An optical disk is recorded with an FM modulated signal having a carrier frequency of 22.05 kHz and a frequency deviation of .+-.1 kHz, as data of 3150 bit/s at a bi-phase clock of 6.3 kHz. A wobble signal can be detected from a rotating disk as a tracking push-pull error. Center frequency components of the wobble signal are detected, and a spindle control is performed in accordance with detected control information. In order to realize a high precision spindle control, the control information is derived from the wobble signal by using a narrow band (high Q) band-pass filter BPF. If the center frequency of the wobble signal shifts to the outside of the band of BPF such as when a spindle starts rotating or during a search, no output is obtained from BPF. It is therefore necessary to control the spindle rotation at a high precision by using an external FG signal and pick position information until the center frequency of the wobble signal enters the band of BPF.
FIG. 3 is a block diagram showing the structure of a spindle circuit system for a conventional optical drive system. A reproduction signal is picked up from an optical disk 1 by a pickup 3. A wobble detector 4 detects a wobble signal from the reproduced signal. The detected wobble signal is supplied to a band-pass filter 5 to obtain information for the spindle control. A CLV controller 8 performs a constant linear velocity (CLV) control in accordance with the control information from the band-pass filter 5 and a standard clock from a standard clock generator 9.
A pick position detector 13 detects pickup position information from a reproduction signal picked up by the pickup 3. An FG detector 14 detects FG information from a spindle motor 2. A rotation detector or controller 15 receives the pick position information, FG information, and standard clock signal, and outputs a spindle control signal for the rotation control.
A selector 11 controlled by a micro-processor 12 selects a control signal from the rotation controller 15 until a predetermined linear velocity is obtained, and selects a control signal from the CLV controller 8 after the predetermined linear velocity is obtained. In accordance with a control signal outputted from the selector 11, the rotation of the spindle motor 2 is controlled.
A spindle control circuit of a conventional optical disk drive performs a spindle control in accordance with center frequency information of a wobble signal obtained by a band-pass filter. Therefore, the center frequency information cannot be obtained until a linear velocity reaches a predetermined value, causing a velocity off-control. In view of this, it is necessary to control the spindle rotation at a high precision by using other information such as FG information and pick position information until the center frequency of the wobble signal enters the band of the band-pass filter. As a result, a precision of an output of the band-pass filter cannot be improved more than an externally controllable precision, thereby limiting the control precision.